A single fiber bi-directional optical module that enables to transmit an upstream optical signal and receive a downstream optical signal with respect to the single fiber has been known as an optical module for an optical communication system. The single fiber bi-directional optical module provides an optical transmitting unit, an optical receiving unit, a fiber securing unit, a housing that assembles the optical transmitting unit, the optical receiving unit, and the fiber securing unit therewith, and a splitting filter that splits an optical signal subject to the optical transmitting unit from another optical signal subject to the optical receiving unit. The housing of the optical module installs the filter holder that secures the splitting filter therein. The filter holder provides a filter mounting surface, which makes an angle of about 45° with respect to an optical axis of the fiber securing unit, that of the optical transmitting unit, and that of the optical receiving unit, on which the splitting filter is mounted.
The optical module thus described provides no mechanism to determine a rotational angle of the filter holder with respect to the housing; accordingly, the filter holder is optionally rotatable. When the filter holder rotates, the wavelength splitting filter mounted on the filter mounting surface deviates the angle thereof with respect to the optical axes from the designed angles, which degrades not only the splitting function of the splitting filter but the optical coupling efficiencies between the optical fiber and the optical units.
The present invention provides an optical module, which transmits and receives optical signals having wavelengths different from each other to and from a single optical fiber, and provides a wavelength splitting filter that splits the optical signals, may assemble those optical components including the optical fiber without carrying out the optical alignment against the housing that installs the wavelength splitting filter therein.